We mainly use BEA staple guns here at work model 16-436LN to be exact that has a 2 inch nose for hard to reach area's a long with a few older Fasco and Senco guns..
They all use 3/8" crown staples from 3/16" to 5/8" Monel or stainless steel staples..
Those are used for everything from headliners, sealers, trim, upholstery and seating.
The BEA's are spendy at around $200 but they come with a parts catalog and can be rebuilt even though we havent had any problems with them after daily use.
It sounds like you are going to be doing stuff steadily for the long hull so I wouldn't skimp out on a staple gun because if you are doing any repair work on newer boats you will probably be reupholstering on seat frames made out of composites like King Starboard, Starlite, Exanded PVC & Ect or even molded..
Those materials are not the same density as MDF, Partical board, Lauan and ect.. and some of those guns like the Porter Cable that are made for stapling through light wood from my experience will not last very long